It is known to use stock-removing tools which are designed and arranged on a rotary tool body so as to straddle the tooth element of a gear type of workpiece. With this arrangement, it is possible to present two stock-removing portions of a tool to a workpiece to thereby simultaneously form or finish a single tooth of the workpiece. The two stock-removing portions are arranged in concentric circular paths so that the rotating tool can be brought into engagement with a workpiece to generate a desired tooth form or shape on the workpiece.
It is also known to use special grinding compositions for tools of the type contemplated herein, and one composition of special interest to present day technology is one that uses cubic boron nitride (CBN) as its essential stock-removing ingredient. CBN grinding wheels offer the possibility of higher metal removal rates and grinding of materials which are more difficult to machine than have been handled with prior grinding equipment and processes, but it is a known problem with CBN grinding that it is very difficult to renew the active surfaces of the CBN grinding wheels after they have been used for a sufficient length of time to deteriorate the surface profile or condition. Generally, renewal of grinding wheel surfaces involves such things as reshaping of profile of the surface, correction of its geometry, and renewal of abrasive particles contained within the surface. All of these treatments are generically referred to as "dressing" of a grinding wheel surface. Cubic boron nitride, as used in grinding wheels, is by its natural characteristics a very hard and difficult material to shape or dress. This problem is especially acute with grinding wheels which are designed to present two annular stock-removing surfaces in a side-by-side relationship on the face of a rotary tool because the active surfaces of such grinding wheels are relatively inaccessible to dressing devices. Accordingly, it is an important purpose of the present invention to provide a design of rotary tool which makes it easier to dress and renew stock-removal surfaces when the tool is formed from cubic boron nitride. However, some of the features of the tool assembly of the present invention will be found to be useful for other types of stock-removal surfaces, and therefore, the invention is not limited to only those tools which utilize CBN as a primary stock-removal composition.
In accordance with the present invention a rotary grinding tool for grinding bevel and hypoid gears and similar workpieces is characterized by an assembly of components which are arranged to permit easy disassembly and separate dressing or renewal of each of the annular grinding elements included in a tool of this type. This is accomplished by providing separate disc-shaped bodies for carrying the two annular grinding elements associated with the rotary tool. A first disc-shaped body is designed to carry an inner stock-removal element of the tool, and a second disc-shaped body is designed for carrying an outer stock-removing element of the tool. The first and second disc-shaped bodies are shaped and dimensioned to be secured together in a way which provides precise concentricity of the inner and outer stock-removing elements relative to each other. In addition, a ring member is provided around the two bodies to give added support and rigidity to the entire assembly. The basic components are secured together with releasable elements which can be easily removed so that either of the first or second annular grinding elements can be dressed and renewed in situ on their respective disc-shaped bodies by an appropriate dressing mechanism. This permits precision renewal of all critical grinding surfaces without interference with parts of the grinding wheel assembly which might otherwise be in the way of the dressing mechanism.
Another purpose of this invention is to provide for a rotary grinding tool which can be easily adjusted to operate with either one or two annular grinding elements.
In a specific embodiment of the invention, the first disc-shaped body includes a recess about its outer periphery for receiving a base portion of an annular grinding element while leaving a stock-removing surface of the element projecting outwardly from the face of the disc-shaped body. This first disc-shaped body includes a bore through its center, and a tapered section is provided in said bore for aligning, very accurately, the first disc-shaped body with a part of the second disc-shaped body which is designed to fit into that portion of the bore. Alternatively, the first disc-shaped body can be accurately mounted directly onto the tool spindle of a grinding machine. The second disc-shaped body likewise includes a bore through its center and, in addition, includes a projecting annular sleeve which is concentric with its center axis for being received into the tapered section of the bore of the first disc-shaped body. In this manner, the two basic components of the assembly can be precisely realigned and centered after a dressing operation has been completed and the components are reassembled for further use on a grinding machine.
These and other features of the invention will become apparent in the more detailed description which follows. In that description, reference will be made to the accompanying drawings as briefly described below.